Small to medium agaric, growing on the ground, litter or wood, with a white or cream spore print. Pileus white, pale, brown, red or pink, purple or grey, not viscid. Lamellae adnexed, adnate or rarely subdecurrent. Stipe central or rarely excentric or lateral. Partial veil remnants absent. Spores hyaline, non-amyloid, smooth; germ pore absent. Cheilocystidia present. Lamellar trama regular. Pileipellis a cutis or a trichoderm, often with branched or nodulose hyphae. Clamp connections present.

Larger species of Marasmius can be quite similar in macroscopic appearance and texture, but they have a hymeniform pileipellis and often the pileus trama is dextrinoid. In addition, the stipe of Marasmius is often smooth and completely dark (to black), at least below the apex, whereas in Gymnopus the stipe surface is often (although not always) hairy. In Rhodocollybia the stipe is always smooth, and the spores are dextrinoid. Tetrapyrgos has triangular or nodulose spores. Marasmiellus affixus, which has a lateral or excentric stipe, is lichenised (growing in colonies on an algal mat on wood) and has a very disagreeable odour. Species of Gymnopus with a markedly excentric or lateral stipe (such as formerly placed in Marasmiellus) are sometimes similar to Campanella, which has a lateral or absent stipe. However, Campanella combines widely-spaced, intervenose lamellae with a gelatinised pileus trama.

Gymnopus (Pers.) Roussel, Fl. Calvados, 2nd edn, 62 (1806).

Micromphale Gray, Setulipes Antonín.

Probably at least several dozen species, although few are as yet formally included in the genus: Gymnopus aff. alkalivirens (= Collybia), G. dryophilus (= Collybia), G. foetidus (= Micromphale, Marasmiellus) and G. villosipes (= Collybia).

The following species are currently placed under Collybia, Marasmiellus or Micromphale but they probably belong in Gymnopus: Collybia endota, C. eucalyptorum, C. kurara, C. nijerria and C. pinacolens; Marasmiellus candidus, M. delicus, M. kindyerracola and M. rawakensis; and Micromphale australiensis, M. miramirildinum and M. rugosum.

A number of species currently in Collybia (C. alutacea, C. moola, C. percava, C. subdryophila and C. yerilla), which mostly lack cheilocystidia (or else they are unbranched), are not disposed to either Gymnopus or Rhodocollybia due to the absence of information on diagnostic characters.

Marasmiellus affixus (pleurotoid, with a strong odour) is keyed out separately.

W.A., S.A., Vic. and Tas. (and probably also N.T., Qld and N.S.W.).

In native forest, and also in gardens, lawns and in plantations under Pinus.

On the ground (usually amongst litter) or attached to litter or wood.

Saprotrophic.

Desjardin, D.E., Halling, R. & Perry, B.A. (1997), Gymnopus villosipes - a common collybioid agaric from California, Mycotaxon 64: 141–147. [Description, B&W Illustration and Microcharacters of G. villosipes]

Fuhrer, B. (2005), A Field Guide to Australian Fungi. Bloomings Books, Hawthorn. [Description and Illustration of G. dryophilus (as Collybia), Marasmiellus candidus, Marasmiellus foetidus and Collybia eucalyptorum]

Grgurinovic, C.A. (1997a), Larger Fungi of South Australia. The Botanic Gardens of Adelaide and State Herbarium and The Flora and Fauna of South Australia Handbooks Committee, Adelaide. [Description and Microcharacters of G. villosipes, Collybia endota, C. eucalyptorum, C. kurara, C. nijerria (also Illustration), C. pinacolens, Marasmiellus kindyerracola, Micromphale australiensis, M. miramirildinum and M. rugosum, and see Key to South Australian species of Collybia and Micromphale]

McCann, I.R. (2003), Australian Fungi Illustrated. Macdown Productions, Vermont. [Illustration of Collybia eucalyptorum, and also of several unnamed Collybia and Marasmiellus species that also quite possibly belong Gymnopus]

Pegler, D.N. (1986), Agaric flora of Sri Lanka, Kew Bull., Addit. Ser. 12: 1–519. [Description, B&W Illustration and Microcharacters of Marasmiellus delicus and 16 other species of Marasmiellus along with Key]

Pegler, D.N. & Young, T.W.K. (1989), The genus Anthracophyllum (Tricholomataceae Tribe Collybieae), Mycol. Res. 93: 352–362. [Description, B&W Illustration and Microcharacters of Marasmiellus rawakensis]

Singer, R. (1973), The genera Marasmiellus, Crepidotus and Simocybe in the Neotropics, Beih. Nova Hedwigia 44: 1–517. [Description and Microcharacters and some B&W Illustrations of numerous species of Marasmiellus and Key]

Wilson, A.W., Desjardin, D.E. & Horak, E. (2004), Agaricales of Indonesia. 5. The genus Gymnopus from Java and Bali, Sydowia 56: 137–210. [Key, Description, B&W Illustration and Microcharacters of 24 species of Gymnopus from Indonesia]